From 447a3643c69b9ed8cd6a80dd99ecc5299ea4e02a Mon Sep 17 00:00:00 2001
From: Dallin Romney <dallinromney@gmail.com>
Date: Wed, 20 May 2026 11:26:14 -0700
Subject: [PATCH] fix(errors): dedupe identical messages when traversing error
 .cause chain (#84556)

Merged via squash.

Prepared head SHA: 46aa27fa12e8e161cddc3c8b901a5dd6851423ca
Co-authored-by: RomneyDa <6581799+RomneyDa@users.noreply.github.com>
Co-authored-by: altaywtf <9790196+altaywtf@users.noreply.github.com>
Reviewed-by: @altaywtf
---
 src/infra/errors.test.ts |  7 +++++++
 src/infra/errors.ts      | 15 +++++++++++----
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/src/infra/errors.test.ts b/src/infra/errors.test.ts
index 4f7a6550d25..e2b6e856c9a 100644
--- a/src/infra/errors.test.ts
+++ b/src/infra/errors.test.ts
@@ -88,6 +88,13 @@ describe("error helpers", () => {
     expect(formatted).toBe("error A | error B");
   });
 
+  it("dedupes repeated cause messages while preserving deeper distinct causes", () => {
+    const rootCause = new Error("provider auth lookup failed");
+    const inner = new Error('No API key found for provider "openai-codex".', { cause: rootCause });
+    const wrapper = new Error(inner.message, { cause: inner });
+    expect(formatErrorMessage(wrapper)).toBe(`${inner.message} | ${rootCause.message}`);
+  });
+
   it("redacts sensitive tokens from formatted error messages", () => {
     const token = "sk-abcdefghijklmnopqrstuv";
     const formatted = formatErrorMessage(new Error(`Authorization: Bearer ${token}`));
diff --git a/src/infra/errors.ts b/src/infra/errors.ts
index b34c6cfae63..b9f62dd3236 100644
--- a/src/infra/errors.ts
+++ b/src/infra/errors.ts
@@ -72,15 +72,22 @@ export function formatErrorMessage(err: unknown): string {
     // Traverse .cause chain to include nested error messages (e.g. grammY HttpError wraps network errors in .cause)
     let cause: unknown = err.cause;
     const seen = new Set<unknown>([err]);
+    // Skip causes that repeat a message already emitted (e.g. coerceToFailoverError).
+    const seenMessages = new Set<string>([formatted]);
+    const appendCauseMessage = (message: string): void => {
+      if (!message || seenMessages.has(message)) {
+        return;
+      }
+      formatted += ` | ${message}`;
+      seenMessages.add(message);
+    };
     while (cause && !seen.has(cause)) {
       seen.add(cause);
       if (cause instanceof Error) {
-        if (cause.message) {
-          formatted += ` | ${cause.message}`;
-        }
+        appendCauseMessage(cause.message);
         cause = cause.cause;
       } else if (typeof cause === "string") {
-        formatted += ` | ${cause}`;
+        appendCauseMessage(cause);
         break;
       } else {
         break;